This invention relates to cartons such as those used as containers for food in which the food can be heated or cooked in an oven.
Cartons which are used to store food or other items which must be heated before they are consumed are usually lined with a tough ovenable plastic liner which may be made from a polyester film or the like. This liner serves to make the paperboard waterproof so that it will not absorb fluids which are stored within the container. Because of the presence of this liner, however, considerable difficulty is experienced in attempting to tear the lid in order to open the tray.
In one prior corner construction, the continuous score line which is formed in the upper face of the lid is spaced inwardly from the side edges of the lid so that it is located inwardly of the flange which supports the lid and the weakened score line which is formed on the lower face is located inwardly from the score line of the upper face in a spaced parallel relationship thereto. In addition, the weakened score line which is formed on the lower face and which extends inwardly from the corner terminates short of the weakened score line which is formed on the upper face. It has been found that this structure is difficult to open because of the difficulty experienced in rupturing the tough film of plastics material which is applied to the inner face of the lid.
In another known structure, a pair of spaced parallel crease lines extend inwardly from the corner on both the upper face and the lower face to form a tab. This tab forms an awkward obstruction which makes it difficult to pore liquid contents out of the vent passage which is formed by depressing the tab. In addition, difficulty is again experienced in attempting to rupture the plastic liner which is applied to the lower face of the lid because the weakened score lines do not extend to the inner weakened score line which is formed on the lower face.
It is an object of the present invention to provide a simple arrangement of weakened score lines on the lid of a tray which will facilitate the tearing of the lid in order to vent and to open the container.